The idea of sign, σημα (sema), has been popular in philosophy and the history of the sciences. Hippocrates and the Stoics, Plato and Aristotle, Saint Augustine and Descartes, Leibniz and Locke, Hegel and Humboldt figure among those who have dealt penetratingly with it. It has engendered a wide variety of sciences and disciplines: semiology, semiotics, semasiology, semantics, sematology which changed their name and content with the influence of time and sometimes of fashion, becoming forgotten to reappear with the impetus of a great thinker. The history of the sciences of the sign deserves systematic study. We shall content ourselves to point out that, of the terms quoted above, semiotics and semiology (or semeiology) have had a longer and richer career than the others. Since Greek antiquity they were applied to two apparently distant fields: military art (the science of manoeuvring troops with the help of signals) and medicine, in which they showed a greater perseverance. In many countries, throughout the 19th century and even today, medical study of the symptoms of illnesses is called semiology.